The present invention relates to presses used for curing pneumatic tires and, more specifically, it concerns the bladder mounted on the press and the mechanism used for the operation of the press.
It is known that to cure hollow articles of elastomeric or plastomeric material having a relatively thin wall, curing molds are used which are formed by at least two hollow halves, mutually engageable and disengageable, able to allow the insertion and the subsequent removal of the article being cured, which, when the mould is closed, presents an outwardly closed cavity, defining the external shape of the article itself.
Inside the mould a bladder is provided, constituted by a flexible envelope, generally made of cured elastomeric material, reinforced if desired, with textile or metal cords, which is inflated by a fluid under pressure at a high temperature. By virtue of the inflation fluid, the bladder expands against the internal surface of the article being cured, thus pressing the wall of the latter against the inner surface of the mold until to the end of the curing cycle.
When the curing cycle is over, the bladder is deflated or placed under vacuum to reduce its overall size, so that the removal of cured article from the mould, which has been opened in the meantime, is facilitated.
All of the movements necessary to open or close the mold and to operate the bladder are carried out by means of a machine of well known structure, known as a curing press.
For the sake of clarity and simplicity and in view of a better understanding, the invention will be described with specific reference to the presses used to cure pneumatic tires, although it is clearly evident from the previous introduction that the invention itself is not restricted to this machine to obtain this specific product, but concerns all the range of machines which comply with the above indicated requirements.
The conventional press used for curing pneumatic tires is well known. Substantially, it is formed of a base and of an upper frame, movable with respect thereto. The base carries a curing mould constituted of two opposite coaxial hollow elements, one fixed to the base and the other connected to a frame, which, in position of assembly (press and mold closed), define a cavity which reproduces the outer toroidal surface of the tire being cured.
Sometimes, in the mold, the two hollow elements have the shape of two annular plates corresponding to the tire sidewalls and the mold comprises a plurality of sectors, arranged circumferentially and inserted between the plates, which are connected to the frame by an annular device with inclined plates, so as to be radially movable in both senses with respect to the two annular plates and axially movable in both senses with respect to at least one of the plates.
Irrespective of the type of mold used, the presses concerned by the invention are provided with a bladder arranged coaxially inside the hollow elements or the annular plates and necessary for the admission of fluid under pressure inside the tire being cured, whose operation is controlled by an actuation mechanism permanently housed in the base.
Although the bladder is actually the only flexible envelope, in the present specification as set forth hereinafter and in the appended claims the expression "bladder", for simplicity's sake, will indicate the assembly formed by the flexible envelope and the two end clamps which block the envelope and guide its shaping during the press working cycle. The flexible envelope, by itself, will be referred to as the "cylindrical sleeve", such being substantially its shape in a rest condition.
It is known that the bladder must be replaced with a certain frequency during the press working cycle, owing to its natural wear or for accidental causes depending on the severe working conditions, or when the mould is to be changed, because the size of the tire being cured changes.
Also, it is known that all of the operations necessary to change the equipment are to be carried out manually and are consequently long and expensive, since it is necessary to await for press cooling before effecting the equipment substitution and then to bring the press back to the pre-established temperature before re-starting the curing operation.
Therefore, it can be easily understood how deep is the interest of the technician in a machine and apparatus which would permit automatic replacement of the equipment and immediate operation after the end of a curing cycle, namely on the press still at a high temperature.
In fact, studies were conducted with reference to mold substitution; however, the problem was not completely solved since the automatic replacement of the bladder did not yet find a convenient solution.
SUMMARY OF THE INVENTION
In accordance with the present invention a new type of bladder, together with its relative operation mechanism, is disclosed by means of which the above problem can be considered as completely overcome, since the replacement of the bladder takes place quite automatically on the machine in a very short time interval, while the machine is still hot, so that cooling experienced by the press and the mold during replacement is of a moderate amount and idle time is not required to again reach the curing temperature.
The present invention aims at providing a bladder and the corresponding mechanism for this operation, which is able to permit an expedited engagement and disengagement of the bladder with respect to the mechanism.
Accordingly, a first object of the present invention is represented by a bladder comprising a substantially cylindrical, flexible and elastically deformable sleeve provided with beads on each end, a movable clamp to block one end of the sleeve and a fixed clamp to block the other end of the sleeve, the movable clamp comprising a disc provided with a coaxial hub and a first fastening ring secured to the disc, the disc and the ring having a peripheral portion of their surface which can be associated with a first bead of the sleeve, and connecting means to block the first bead between the disc and the ring, the fixed clamp comprising a pair of distinct coaxial elements to be firmly secured together, each element having an annular portion of its surface which can be associated with the second bead of the sleeve, and a connecting means to block the second bead on the fixed clamp, the bladder being characterized in that it includes devices for the automatic engagement and disengagement of the movable and fixed clamps with respect to a corresponding supporting and operating mechanism.
A second object of the invention, in any case inseparable from the above cited first object of the same, is represented by a supporting and operating mechanism for the bladder, the mechanism comprising a support to be associated with the fixed clamp of the bladder and a stem, coaxial with the support, axially slidable into it, to be associated with the movable clamp of the bladder, and means to carry out the axial displacement of the stem with respect to the support, the mechanism being characterized in that the support and the stem are provided with devices for the automatic engagement and the disengagement of the movable and fixed clamps.
According to an appropriate embodiment of the invention, the devices comprise an annular groove obtained on the radially inner surface of the movable clamp and another annular groove obtained on the radially outer surface of a flanged tube which represents one of the two elements constituting the fixed clamp, the other element being constituted by a ring fastening the bead, which can be integrally associated to the flanged tube.
Correspondingly, the devices provided on the mechanism actuating the bladder according to the invention comprise a plurality of pegs, housed into corresponding holes, positioned both on a head fast or integral with the end of the stem which is to be associated to the movable clamp, and on the support which is to be associated with the fixed clamp, the pegs being radially movable in both senses, in a plane perpendicular to the axis of the mechanism, between two positions, namely an expanded or work position and a collapsed or rest position, respectively, means being provided to move the pegs from the collapsed to the expanded position, the pegs in the expanded position being at least partially protruding from the lateral surfaces of the head and of the support which face the corresponding surfaces of the hub and of the flanged tube and being housed in the corresponding annular grooves obtained on the hub and on the flanged tube.
In a preferred embodiment, the head integral or fast with the stem and associable to the movable clamp is cup-shaped. Its lateral wall is provided with radial holes, whose axis lies in a plane perpendicular to the axis of the stem, to house corresponding pegs alternatively movable radially between the expanded position and the collapsed position, the pegs being provided, on their end directed towards the cup inside, with two axially opposite wings, the motion of the pegs between the two positions comprising a rotation around one of the wings, the cup containing an axial small piston, shaped as an overturned goblet and axially slidable inside the cup, contrast means being provided to prevent the small piston from exiting the cup and elastically deformable means being provided to control the axial motion of the small piston with respect to the cup.
Further, the means causing the motion of the pegs from the collapsed to the expanded position are conveniently represented by cam profiles obtained on elements coaxial with the axis of the mechanism and revolving about their own axis, as for instance a cam encased inside a cup-shaped head, integral with the stem end, associated to the movable clamp, and a ring nut revolving about an annular flange fast with the support, the latter being provided with a coaxial bush comprising the pegs, radially displaceable to be associated to the fixed clamp.
Vice versa, in the head to be connected to the movable clamp, carried out according to the preferred embodiment, the displacement of the pegs from the collapsed to the expanded position is driven by the relative axial movement of the small piston.
Finally, the bladder according to the invention comprises devices, as for instance further annular grooves obtained on the radially outer surfaces of the movable and fixed clamps, in order to be picked up, transported and released, in a completely automatic manner, by appropriate pliers having gripping arms at least radially movable in both senses but, preferably, also axially movable in both senses with respect to the axis of the pliers .